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Hungary Bill
Hungary Bill GRM+ Memberand Reader
6/29/12 2:56 p.m.

I would run it light as a feather and take the horse power penalty.

Extra weight means extra stress on the other components (brakes, tires, clutch, shocks, etc etc etc.) I really think that the lighter car will be more nimble in the turns, be able to brake later, and would provide better feedback to the driver.

if the car was "squirley" in the turns maybe a well placed wing would be in order, but I would try my best to avoid ballast.

Ranger50
Ranger50 SuperDork
6/29/12 3:03 p.m.

I'm going for torque given the MM Mustangs in AI. Of the engine builds they allow to be printed in the mustang rags, they always built for torque as HP was penalized. They only made like 350hp, but made 25 extra ft/lb of torque then the next guy.

scardeal
scardeal Dork
6/29/12 3:04 p.m.

Well, if you're building to a specific P/W ratio, and, considering that you're using the same chassis to do so, you could do like the NASCAR guys do, and make the undertray the ballast. So, you'd effectively be able to make the CG on the heavier car significantly lower than the CG on the lighter car. Plus, you could easily fine-tune the front/rear, left/right weight distribution without messing with ride heights.

Even more fuel on the fire.

pimpm3
pimpm3 Reader
7/1/12 2:39 a.m.

Everyone is over analyzing this. The question is how does weight / power effect handling / speed given a constant power to weight ratio.

Take a car an e36 M3 for example: Measure acceleration / g / lap time etc. Weigh and dyno.

Strip out car say 500lbs for example, figure out a way to restrict engine to the appropriate power level / power to weight and re-test. Everything else stays constant ie tires, etc... that way you are only comparing how the power to weight is acheived.

Extraplolate from there.

Now that I think about it it may be easier with a turbo car since the power can be adjusted through boost level.

Maybe this could be worked into the test of the new GRM $2012 WRX wagon. It is free to pull things off of a car...

seeker589
seeker589 Reader
7/1/12 9:12 a.m.

This is a very valid argument. I must agree with the "course configuration" variable.

My experience is that tight courses reward less weight. I beat the snot out of Corvettes at a local Corvette club autocross with my stock GLH turbo - but got trounced on an wide open course. Applicable torque, momentum, tire warm-up, and weight transfer management. On tight courses - inertia becomes your enemy as vehicle weight increases.

This can be explored virtually on Gran Turismo, Forza, or iRacing programs- as it was posted prior. Given the growing acceptance of virtual mediums - this could make a great article comparing and contrasting the gaming platforms. It could also be used to promote virtual racing in general. Potential advertisers are out there.

In other words - I would be interested in reading an article using virtual racing mediums comparing these variables.

Anyone else?

Argo1
Argo1 Reader
7/1/12 9:14 a.m.
pimpm3 wrote: Take a car an e36 M3 for example: Measure acceleration / g / lap time etc. Weigh and dyno. Strip out car say 500lbs for example, figure out a way to restrict engine to the appropriate power level / power to weight and re-test. Everything else stays constant ie tires, etc... that way you are only comparing how the power to weight is acheived.

It actually is a bit more complicated than that. With big weight changes, the spring rates and such are no longer optimum for the new weight and will effect the results. This is where computer simulations can give more accurate results with the chassis optimized for each test weight/ power.

corytate
corytate Dork
7/1/12 9:22 a.m.
EvanR wrote: Do I get to pick the course? For a single run on a short autocross, I shall skip the ICE entirely and build an electric car with just enough battery to get around the course once. Instant, consistent torque trumps all.

so the answer is found: 80hp/1000rpm engine (400ft/lbs) =] in an 800 lb car.
engine will take up a third of that weight though=/ lol

Giant Purple Snorklewacker
Giant Purple Snorklewacker UltimaDork
7/1/12 9:22 a.m.

In reply to Argo1: +1

Suspension and brakes should be designed for the tire choice, lower weight and ride height, and any aero that will be added. You don't need a computer sim to think it thru but it sure would be helpful and time/cost effective if you have access to such things.

DWNSHFT
DWNSHFT HalfDork
7/1/12 2:36 p.m.

Why reinvent the wheel? Go to the NASA championship event and survey the field of the classes that run an open rule set but a specified power-to-weight ratio. This gives you lots of data points without spending much money. You have the driver variable but you can hold weather and track constant.

David

pimpm3
pimpm3 Reader
7/1/12 4:17 p.m.
Argo1 wrote:
pimpm3 wrote: Take a car an e36 M3 for example: Measure acceleration / g / lap time etc. Weigh and dyno. Strip out car say 500lbs for example, figure out a way to restrict engine to the appropriate power level / power to weight and re-test. Everything else stays constant ie tires, etc... that way you are only comparing how the power to weight is acheived.
It actually is a bit more complicated than that. With big weight changes, the spring rates and such are no longer optimum for the new weight and will effect the results. This is where computer simulations can give more accurate results with the chassis optimized for each test weight/ power.

I realize it is more complicated then that as much as the next guy. The reason I propose to use the same car, is that it keeps everything else constant. You have to control the other aspects of the equation or the whole test gets out of hand. As many of the other posters have pointed out, tires, suspension geometry, aero etc.. effect the results. By using the same vehicle that is not the case, the only thing in play is the weight and the power with a constant power to weight ratio.

MadScientistMatt
MadScientistMatt SuperDork
7/1/12 4:28 p.m.

A good example of how this can be extremely course dependent - look at the Bonneville cars. Some weigh as much as a Suburban in race trim so they can get good traction on the salt and not get blown around by aero effects.

JG Pasterjak
JG Pasterjak Production/Art Director
7/1/12 4:44 p.m.

Yeah, there's certainly a ton of variables, I'm just wondering if you can standardize things enough to draw some conclusions. Personally, I would love to see the shape of the curve defined by a graph of lap times of a car as weight and power increased.

My guess is that the curve would start out steep, as the low horsepower struggled to overcome even modest aero friction. Then I think it would level out for a bit. I have a feeling that the difference between, say, a 2500lb car with 250hp and a 3000lb car with 300hp would be relatively minor. Then I think the graph would drop rapidly again as the tires became overwhelmed by the extreme weight of the car and no mount of power could overcome it.

jg

Anti-stance
Anti-stance Dork
7/1/12 4:55 p.m.
seeker589 wrote: This is a very valid argument. I must agree with the "course configuration" variable.

I would think two cars(one light/low hp and one heavy/high hp) may produce different outcomes depending on the track.

I would assume the heavy/higher hp car would benefit from the long straight-aways at a course like Road America with a good part of that being from the inherent torque advantages that come with larger engines.

I would also think that the lighter/low hp car would do great in an autocross or moderate road course.

This would be assuming that they had the same dimensions, weight distribution, drivetrain layout, and punched the same hole through the air.

What about tire size? Would that be the same between the two?

corytate
corytate Dork
7/1/12 9:37 p.m.

A way to do the article:
Follow a series running power/weight ratio rules to different styles of tracks.
Pick three or four different competitors with different solutions (lightweight low powered car, big powerhouse, etc etc) and do sections on each team after each race, how it drove, how it stacked up against the others, etc etc)
=profit

wheels777
wheels777 Dork
7/2/12 7:34 a.m.

A low HP high torque engine will be easier to find in a heavier package. Light lower HP engines typically don't make a lot of torque. But a small package can apply more HP to accelleration and less to fighting aero drag. Need more data to compute. But cost, chassis efficiency, torque vs HP, I would bet on something in the 2800-3300# range.

fasted58
fasted58 UltraDork
7/2/12 7:49 a.m.

For the 1000lb/ 100hp model all I can come up w/ is a 750cc Formula 4, D/SR w/ older engine packages or maybe B Mod. I'm really diggin' that formula but how ya really gonna compare that to the 4000lb/ 400hp car, i.e. a formula or SR chassis to a sedan (most likely)? Apples to oranges.

Brett_Murphy
Brett_Murphy GRM+ Memberand Dork
7/2/12 12:30 p.m.
Giant Purple Snorklewacker wrote:
Sky_Render wrote:
Giant Purple Snorklewacker wrote: Torque.
This. SOMETIMES.
That. ALWAYS.

SOMETIMES, maybe even almost always. However, if you're doing rallycross, once you've got enough power to spin your tires, everything else is wasted. Better tires and driver skill are going to make a much bigger difference.

If I was driving and all other things were equal and the power to weight ratio were adjusted to also be the same, I'd prefer an E30 318i over a 325i for rallycross.

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